From: "James Clarke" Subject: Internet Geology News Letter No. 28, January 17, 2000 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Unsent: 1 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 News Letter No. 28, January 17, 2000

Deltaic Deposits of Sea of Okhotsk Region
Internet Geology News Letter No. 28, January 17, 2000

Deltaic deposits are present on the continental side of the
Sea of Okhotsk and possibly also west of Kamchatka. There
were two stages in the formation of these deltas: Paleogene
and Neogene. The Paleogene was characterized by retreat
of the deltas toward the continent and attendant onlap of deep-
water marine clayey and clayey-siliceous deposits on the
deltaic sediments. The Neogene was characterized by advance
of the deltas toward the sea with corresponding replacement of
the deep-water marine facies by shallow-water marine and
continental facies. The Amur-North Sakhalin is the best known
of these deltaic zones and is described here.

Lithofacies distributions indicate that a river system was
active over a long period of time northwest of Sakhalin Island
in the area of theTatar Strait and the Amur Estuary.
Its effect was felt even in Cretaceous time when deltaic
coal-bearing sediments were deposited in the Aleksandrov
region of Sakhalin. It has long been recognized that the
sedimentary rocks of North Sakhalin are delta deposits of the
paleo-Amur River.

Drilling in the northwest part of North Sakhalin has not
disclosed any significant amount of Paleocene and Eocene
sediment; transport of clastics from the continent was minimum.
At the same time much clastic material was introduced into the
area at the north end of the Tatar Strait to be transported from
north to south along the Tatar Strait. Volcanic activity associated
with a Lower Amur graben intensified in Eocene time, covering
the area where the estuary entered to basin of sedimentation.

Some 200 km south of the Amur Estuary is the Kizi Estuary,
also the site of a graben, where thickness of the Upper Cretaceous
and Cenozoic exceeds 4000 m.

In Oligocene time clastic material was dumped into the zone
of the modern Amur Estuary. Continental coarse clastic and
coal-bearing complexes collected in the west of Sakhalin. Farther
to the east these pass into sand-clay and clay marine facies.
During subsequent Neogene time thick deltaic sediments
were deposited in the area of the modern Amur Estuary and North
Sakhalin. During the entire Neogene the Kizi paleo-estuary was
the site of uncompensate deposition with collection of marine
clays and siliceous clays (from Petroleum Geology, vol. 29,
no.1/2, p. 54-62, 1995 with 13 lithofacies maps - digested from
Varnavskiy and others, 1990).

Copyright 2000 James Clarke. You are encouraged to print
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